Apple today released iOS 7 beta 4 to developers after a longer than usual delay between builds believed to be the result of a security breach which brought the Developer Center offline for 8 days.

Beta 4, labeled as build 11A4435d, comes exactly 21 days after the release of beta 3. A week later than iOS 7 betas 2 and 3 which were released every two weeks like clockwork.

The new beta release includes a number of enhancements and changes, including a redesigned lock screen, improvements to Notification Center and a cancel button on the search screen according to MacRumors.

The lock screen contains a new Slide to Unlock icon and animation which make it slightly more obvious. It also includes new bar icons to expose Notification Center and Control center.

Notification Center now supports swiping left and right to switch between Today, All and Missed. There is also a new notification for completed uploads.

Perhaps the most immediately visible changes are to the Phone app, including refined Answer, End, Decline, Remind Me and Message buttons.

Another new feature is the ability to set up a completely new Apple TV from an iPhone running iOS 7.

Other news features in iOS 7 beta 4, including changes to Siri, Mail and Messages, are being tracked at MacRumors.